But surely!!.... It will only look effective if your back glass is spotlessly clean? If you have any blemishes then there gonna look like there suspended in mid-air.
Once you get coraline growing on the back imho it will look a bit silly... mind you, i've never actually seen one, i'm just trying to imagine it. What about snails & stars on the back glass, they'll look like their levitating.
In short, I would try and keep your display tank as natural looking as possible... sticking a mirror in is just, well, .... ahem....spooky. :eek1: